Process for making lightweight fired ceramic bodies



United States Patent 3,390,212 PROCESS FUR MAKENG LIGHTWEIGHT FiRlEDCERAMIC BGDIES Russell T. Stella, 6 N. Walnut St, Brazil, Ind. 47834 NoDrawing. tContinuation-in-part of application Ser. No.

372,108, June 2, 1964. This application Nov. 14, 1966,

Ser. No. 593,754

2 Claims. (Cl. 264-44) ABSTRACT OF THE DESCLUSURE A process for makinglightweight ceramic bodies having superior physical propertiesconsisting of grinding and mixing sandy and plastic clay, adding anoil-water emulsion in the amount of from 5 to 30% of the weight of theclay, thoroughly mixing the clay-water-oil emulsion mix, shaping theceramic mix containing the oilwater emulsion by extrusion, by pressing,by hand, or by any other convenient process and firing the resultanttile shapes.

This invention relates to a novel method of manufacturing ceramic bodiesand more particularly, to a meth- 0d of manufacturing lightweightceramic bodies of uniform density, and is a continuation-in-part of mypending application Ser. No. 372,108, filed June 2, 1964, and nowabandoned.

The problem of making lightweight ceramic bodies, such as bricks ortile, has existed in the ceramic industry for decades. One method ofsolving this problem has been to employ a lightweight aggregate such asdiatoma ceous earth or, more recently, vermiculite in admixture with theclay. While the resulting ceramic body was indeed somewhat lighter inweight, it had certain undesirable properties such as lowered impactstrength, and lower breaking strength. Both of these defects wereattributable to the lack of uniformity of the finished product producedby the presence of a lightweight aggregate itself. Furthermore, therewas an inherent limit to the decrease in weight achieved by their usesince only a small percent of the could be replaced if the ceramic bodywere to maintain its coherence after firing.

Another method of forming lightweight ceramic bodies has been to addmaterials to the clay which would burn out during the firing process.For instance, wood chips or sawdust were mixed with the clay powderprior to forming the shaped ceramic mass. Then, during firing, the hightemperatures used ignited the combustible material which eventuallyvaporized substantially completely, leaving only a small amount of ashand, more important, a void in the fired ceramic body where thecombustible material had been. This process too had certain drawbacks.In the first place, uniform mixing of such disparate materials as clayand wood chips was unattainable without the use of extremely expensiveequipment. Secondly, the fired ceramic body was usually not much lightersince the combustible material replaced water which was driven offduring a conventional firing process. Thirdly, many of the cheapcombustible materials when used in relatively large quantities gave anirregular pattern of voids in the ceramic body, resulting again in anon-uniform body of decreased impact or breaking strength.

It is an object of this invention to provide a method of makinglightweight ceramic bodies, which method is economical to operate,requires only conventional equip ment and utilizes cheap, readilyavailable starting materials. It is also an object of this invention toprovide lightweight ceramic bodies of more uniform quality than hithertopossible at a manufacturing cost comparable to Fatenteol June 25, 1%63that for ceramic bodies of conventional density. Other objects Willbecome apparent from the following description.

The process provided by this invention comprises mixing clay with ahomogenized stable oil-water emulsion in which all the oil micelles arecapable of passing a 30 mesh screen, forming the resulting mixture intoa desired shape and then firing the shaped ceramic mass. In the aboveprocess, it is most necessary in the first place that the oil dropletsin the oil-water emulsion be of micellular dimensions; i.e., of a sizecapable of passing a 30 mesh screen; and secondary that the micellularoil particles do not coalesce to any appreciable extent while theoilwater emulsion is being mixed with the clay, or while theemulsion-water-clay mixture is being shaped.

In the above process, the oil-water emulsion replaces part to all of thewater usually employed in the conventional mixing and shaping processesused to form shaped ceramic articles from clay and water. In addition,the micellular oil particles displace from 520% of the clay particlesthemselves which would have been present in a conventional clay-watermatrix. This replacement takes place because the oil particles are ofcomparable size to the clay particles and this dimensional similarityenables the oil micelle to replace a solid clay particle in thewater-clay matrix. Later on, during the firing process, the micellularoil droplets in the clay matrix are burned out and the water in thematrix is removed by evaporation. The resulting fired ceramic body thencontains a series of microscopic voids left by the burning out of theoil in addition to the voids left by evaporation of the water. Theselatter voids would be left in a conventional firing process but thevoids left by the burning out of the oil are in addition to these voids.The voids left by the burning out of the oil can amount to from 5 to 20%of the total volume of the fired ceramic mass which as a consequence,weighs from 5 to 29% less than a conventionally fired ceramic shape,formed from just clay and water.

Needless to say, if the oil is not truly emulsified in the water priorto mixing with the clay, or if the emulsion breaks down during theprocess of mixing the emulsion with the clay, or of shaking theemulsion-clay mixture, the resulting clay-water matrix will have largeglobs of oil distributed unevenly throughout the mass. These globs ofoil will, on burning out during firing, leave large irregular vacancies(as contrasted with the uniform microscopic voids left behind by burningout the emulsified oil micelles). Shaped ceramic masses containing suchmacroscopic vacancies tend to collapse on firing, and the resultingfired ceramic shapes are most unsatisfactory.

As can be seen from the above discussion any tendency of the oilparticles to coalesce and form substantial quantities of droplets havingdimensions ranging from greater than 30 mesh on the low side up tomacroscopic globules on the high side, will defeat the end result of mynovel process, which is as previously stated, a lightweight firedceramic body having a strength comparable to that of a conventionallyfired ceramic body of the same shape. Further, the presence of suchcoalesced macroscopic oil droplets will result in imperfect andmisshaped fired bodies having fissures, holes, the like with a tendencyto crumble under pressure. Surprisingly, the lightweight fired ceramicbodies produced by the process of this invention, even those which are20% lighter than conventionally produced ceramic bodies, having as theydo a series of uniform microscopic voids, have shown no tendency tocollapse during the firing process when extremely high temperatures areencountered.

The clays which I employ in my novel process are those which have beenemployed in the manufacture of ceramic bodies throughout the years, andinclude inert clays, plastic clays and mixtures of these types of clay.The exact nature of the clay employed is not critical and my novelprocess is adaptable for use in all processes which produce firedceramic shapes since the oil-water emulsion replaces all or part of thewater used in the conventional mixing and shaping process. The precisenature of the oil used in the oil-water emulsion is also not criticalprovided only that the oil is combustible and has a flash point above160 F. and below 1700" F. The oil employed should, however, have a highB.t.u. content, say of the order of l50,000-170,000 B.t.u.s per gallon,although oils with higher and lower B.t.u. ratings per gallon are fullyoperative. A preferred oil for use in my novel process is #2 fuel oilwhich has a rating of about 160,000 B.t.u.s per gallon, is readilyavailable in large quantities and is relatively inexpensive.

The emulsifying agents employed in forming the oilwater emulsions usefulin my invention include both ionic and non-ionic surfactants includingalkali metals, ammonium and amine salts of long chain aliphaticcarboxylic and sulfonic acids, of alkyl aryl sulfonic acids; alkyl arylpolyether alcohols, alkyl esters of sodium sulfosuccinic acid, sodiumand potassium salts of sulfate esters of alkyl phenoxy polyoxy ethyleneethanol, distearyl dimethyl ammonium chloride, polyoxy ethylene sorbitanmonolaurate and other surfactants of the type listed in Soap andChemical Specialties, December 1957, JanuaryApril 1958, by John W.McCutcheon.

In carrying out my novel process, a mixture of clays, including bothinert, sandy clay and plastic clay containing water bound bothchemically and physically, is ground and mixed with suflicient water torender the mass plastic. Next, an oil-water emulsion amounting to from30 of the weight of the clay mix is added. Alternatively, the oil-wateremulsion can be added initially to supply all the Water needed informing the plastic ceramic mass. The ceramic mix containing theoil-water emulsion is then shaped by extrusion, by pressing, by hand orby any other convenient process, and the shapes thus produced are fired.The amount of emulsion needed depends both upon the percent of oil inthe emulsion and on the B.t.u. rating of the oil, it being desirablethat the oil be present in a quantity sufiicient to furnish 3,000,000B.t.u.s of heat per ton of clay mix during the firing process.

The use of the oil-water emulsion in place of water in the ceramic mixprior to firing has the added advantage of providing a uniform internalsource of heat provided by the burning oil during the firing rocess.This internal heating is superior to that obtained with any of the othercombustible materials heretofore used in admixture with clay.Furthermore, the use of a uniformly dispersed internal heat source givesa more even and controlled heat throughout the shaped ceramic massduring the firing process since the amount of internal heat can becontrolled by the number of B.t.u.s per ton which the oil of thewater-oil emulsion can furnish. As has been previously pointed out, thenumber of B.t.u.s can, in turn, be controlled by the quantity of oilsupplied to the ceramic mass as an oil-water emulsion and by the B.t.u.rating of the oil.

More specifically, my invention is carried out as follows: 1000 lbs. ofsandy clay and 1000 lbs. of a plastic clay were thoroughly ground andmixed. 40 gallons of a 50% emulsion of #2 oil and water containing inaddition 0.5% of potassium stearate as an emulsifying agent, were added.The oil micelles were capable of passing through a 30 mesh screen. The#2 fuel oil has a flash point or ignition point at about 160 F The claypowder and oil-water emulsion were thoroughly mixed and the mixtureextruded at about 120 F. into bars 4 inches wide and /2 inch high, whichwere cut into 4" x 4" tile shapes.

The green tiles were then fired by slowly heating to a temperature ofabout 2200" F. over a period of hours. The resulting tile is of uniformappearance, has a fine grain structure, weighs about 10% less than asimilar tile manufactured with Water only added to the dry clay mixprior to extrusion, and has the physical properties and characteristicsshown in Table I.

TABLE I Comprehensive strength 2000 p.s.i. Distortion tolerances WithinASTM. Face dimension variation Within ASTM. Bed depth variation WithinASTM. Freeze-thaw 1100 times. Absorption 6%. Color and texture (body)Production grade. Glazing -l Excellent. Face blisters None. F ace chipsWithin ASTM. Autoclave test 'Within ASTM.

The lightweight fired ceramic bodies produced by the process of thisinvention are stronger and more uniform in quality than those producedby the admixture of solid combustible material, such as sawdust withclay powder and water, prior to firing. The greater strength anduniformity is undoubtedly attributable to the microvoids produced byburning the micellular oil droplets which have replaced part of the clayin the ceramic matrix.

While the invention has been disclosed and described in some detail inthe drawings and foregoing description, they are to be considered isillustrative and not restrict-ive in character, as other modificationsmay readily suggest themselves to persons skilled in this art and withinthe broad scope of the invention, reference being made to the appendedclaims.

I claim:

1. The process of making lightweight fired ceramic bodies whichcomprises mixing dry clay powder With from about 5% to about 30% byweight of an oil-water emulsion stabilized with an emulsifying agent andwith sufiicient added water to render the ceramic mass plastic, saidemulsified oil substantially being present at all times during saidmixing process in the form of micellular droplets capable of passing a30 mesh screen, said oil having a flash point in the range of F.-1700 F.and a B.t.u. rating of 130,000 to 170,000, and said micellular oildroplets constituting from about 5% to about 50% of said oil-wateremulsion, forming the thus formed plastic ceramic mass into desiredshapes and firing said shaped ceramic mass, whereby a plurality ofsubstantially uniform microscopic voids are produced in the firedceramic body.

2. The process of claim 1 in which No. 2 fuel oil is added in ,the formof an oil-water emulsion at the rate of 20 gallons of No. 2 fuel oil perton of dry clay mix,

References Cited FOREIGN PATENTS 805,844 12/1958 Great 'Britain.

OTHER REFERENCES Alexander: Colloid Chemistry, vol. VI, 1946, ReinholdPublishing Corporation, New York, N.Y., page 271.

ROBERT F. WHITE, Primary Examiner.

A. R. NOE, LT. A. FINLAYSON, Assistant Examiners.

